Basil Rathbone & Nigel Bruce played Sherlock Holmes & Dr. Watson in fourteen films between 1939-1946. Of these fourteen films, four fell into the public domain according to WikiPedia:
SHERLOCK HOLMES AND THE SECRET WEAPON (1943) http://www.archive.org/details/secret_weapon
SHERLOCK HOLMES - THE WOMAN IN GREEN (1945) (this page) http://www.archive.org/details/TheWomanInGreen_894 (other formats)
SHERLOCK HOLMES - TERROR BY NIGHT (1946) http://www.archive.org/details/Terror_By_Night
SHERLOCK HOLMES - DRESSED TO KILL (1946) http://www.archive.org/details/dressed_to_kill
Of the 4 public domain films (or all 14 for that matter), THE WOMAN IN GREEN is a key film in that the arch-enemy of Holmes, Professor Moriarty, finally gets his just due.